Constructing an energy efficiency benchmarking system for coal production

Constructing an energy efficiency benchmarking system for coal production

Applied Energy 169 (2016) 301–308 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Const...

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Applied Energy 169 (2016) 301–308

Contents lists available at ScienceDirect

Applied Energy journal homepage: www.elsevier.com/locate/apenergy

Constructing an energy efficiency benchmarking system for coal production Ning Wang a, Zongguo Wen a,⇑, Mingqi Liu a, Jie Guo b a b

State Key Joint Laboratory of Environment Simulation and Pollution Control (SKLESPC), School of Environment, Tsinghua University, Beijing 100084, China Department of Electromechanical and Environmental Protection, Yankuang Group Co., Ltd., Fushan South Road, Jining, Shandong 273500, China

h i g h l i g h t s  Contributed to overall coal industry energy efficiency research by focusing on coal mining production.  Constructed an energy efficiency indicator system to benchmark coal production.  Created an energy efficiency benchmarking methodology and defined the benchmark standard.  Analyzed the potential for energy efficiency improvements in China’s coal production.

a r t i c l e

i n f o

Article history: Received 2 March 2015 Received in revised form 3 February 2016 Accepted 4 February 2016

Keywords: Energy efficiency Coal production Energy benchmarking Energy saving potential

a b s t r a c t Coal mining not only produces, but also consumes a large amount of energy. Coal production has an extremely high energy efficiency potential, and benchmarking is critical to discover this potential. To address problems such as ambiguity of coal production (e.g. underground mining), benchmarking range and absence of both indicators and standards for energy efficiency benchmarking, this paper makes use of product-based and process-based benchmarking. These two techniques are used to construct a benchmarking system for coal production with high energy efficiency, and improve the standards used at the eight coal mines owned by the Yankuang Group. Comparison and analysis of benchmarking in enterprises indicates that energy use during raw coal production could be reduced by 22.77%. Across China energy savings from coal production could reach 15.98–32.98 Mtce, with an equivalent 42–87 Mt of CO2 emissions saved. Lastly, this paper provides measures to improve coal production energy efficiency. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction 1.1. Current energy efficiency in the coal industry Research on energy efficiency in the coal industry (coal mining, processing, utilization) primarily focuses on coal processing and utilization, including power generation, chemicals, metal smelting other key industries. For example, Zhang et al. [1] and Bhatt [2] researched the energy efficiency of coal-fired electric power plants; Man et al. [3] designed a coke-oven gas assisted coal to olefins process for high energy efficiency; Zhang et al. [4] proposed improving energy efficiency of cyclone circuits in coal beneficiation plants; Santosh et al. [5] researched clean coal technology to improve environmental quality and energy efficiency. ⇑ Corresponding author. Tel./fax: +86 10 62792921. E-mail addresses: [email protected] (N. Wang), [email protected] (Z. Wen). http://dx.doi.org/10.1016/j.apenergy.2016.02.030 0306-2619/Ó 2016 Elsevier Ltd. All rights reserved.

However, the literature rarely analyzes energy consumption in the coal mining sector, but rather focuses on coal mining in terms of economic benefit. Although there is no documented amount of energy consumed by the global coal mining industry, according to Chinese data it is estimated that energy consumption reached 100 Mtce (million tons of coal equivalent) per year. Some studies show that coal mining has high energy-saving potential: Zhao et al. [6] found that coal mining and washing is one of the fastest ways to increase TFEE (total-factor energy efficiency), meaning a higher level of energy efficiency per unit of economic output. Also, the US Department of Energy (DOE) energy bandwidth analysis shows that the US mining industry consumes about 365 billion kW h/year and that there is potential to reduce the annual energy consumption to 169 billion kW h, which is about 46% of current annual energy consumption [7]. Therefore, research on energy efficiency of coal mining is significant for the entire coal life cycle.

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1.2. Research on energy efficiency benchmarking In a given industry, energy benchmarking is defined as a process of measuring energy performance of an individual plant or sector against a common metric that represents ‘‘standard” or ‘‘optimal” performance of that plant or sector [8]. It is useful for understanding energy use patterns, identifying inefficiencies in energy use, estimating the potential for energy conservation, and designing policies to improve energy economy [9]. Energy management is widely used in a variety of industries, as listed in Table 1, which lists energy efficiency benchmarking management by industry type. With regards to energy intensive industries, previous studies have proposed energy efficiency benchmarking systems on oil and gas chemistry [10], steel industry [11] and cement industry [12]. However, very few studies focused on energy efficiency benchmarking for coal mining, likely due to the complexity of coal production technology and lack of international attention. Though the first process-based coal mine standards were established in 1992 [13], in the past two decades, there has been nearly no research on major energy consumption indicators of coal mine energy efficiency, nor were there any case studies available that describe the status of energy efficiency in coal mining. We have researched on the Science Direct and ISI Web of Knowledge database for the keywords ‘‘coal production”, ‘‘coal mining”, ‘‘energy efficiency” and ‘‘benchmark” from the year 2000 to 2015, but we do not find relevant literatures. Coal production energy efficiency benchmarking is crucial in studying coal energy consumption and therefore, a new benchmarking methodology and a set of energy consumption grade standards need to be established. The traditional method is based on estimates of energy efficiency, which can be expressed as the ratio of energy consumed in coal mining and preparation and the total energy produced. This method is too simple, however, to reflect energy efficiency in coal production, and does not capture the disparity in conditions from different regions of China. Only two provinces have established provincial coal production standards, and they have shown great disparity even in the same year. Shandong’s standard limits the comprehensive energy efficiency from 5.00 kgce/t to 14.53 kgce/t for different mines in 2012 [14], and Liaoning’s provincial standard limits it to 12.4 kgce/t for existing mines in 2012 [15].

Table 1 Energy efficiency benchmarking management application areas. Areas

Research focus

Industrial energy benchmarking

Introduces industrial energy benchmarking and existing programs and practices. Also provides a general description of industrial energy benchmarking [9] Presents a method (mapping & benchmarking) to compare the energy efficiency of products across countries [16] Estimates the best practice technology (BPT) energy use of 17 industry sectors based on energy benchmark curves or energy indicators prepared at country-level [17] A total of twelve methods for benchmarking building energy consumption are reviewed. It is found that many simple methods can achieve satisfactory performance [18] Estimates the minimum energy consumption of total mining industries including coal, metal and minerals using statistical data. Benchmarking analysis is useful to estimate the energy saving potential [19] Conducts a study on the potential for reducing global energy-related CO2 emissions from electricity production through simple benchmarking [20] Provides a baseline for energy in current gold and copper operations internationally [21] Builds a process lifecycle model of enterprise energy efficiency benchmarking and models for indicators of energy efficiency potential to provide the foundation for benchmarking options [22]

Products across countries 17 industry sectors

Building

Mining industry

Electricity production

Copper and gold Enterprise energyefficiency potential

47.4% 35.7%

1.3. The structure of world coal production World coal production in 2012 was 7.8645 billion tons. China has always been a major player in global coal production and consumption. Coal production in China has increased significantly from 917.4 Mtoe (million tons of oil equivalent) in 2003 to 1840 Mtoe in 2013, with an annual growth rate of 7.2% [23]. China’s share of world coal production rose from 35.7% in 2003 to 47.4% in 2013 (Fig. 1). It is predicted that coal will continue to play a leading role in the energy structure of China for a long period [24]. The mining industry is one of the major energy-consuming sectors. It not only generates energy, but also consumes a large amount of power and contributes to greenhouse gas emissions (GHG). Sahoo et al. [19] estimated that energy consumption in the global mining industry accounts for 3% of all global energy consumption across all industries. The total energy consumption in mining sector in China was 211.9 Mtce in 2012 [25], accounting for 8.4% of the total energy consumption, which is much higher than the global average. Specifically for coal mining, the total energy consumed during coal mining increased from 40 Mtce in 2005 to over 60 Mtce in 2012, accounting for 2.4% of all industries in China1. 1

Unpublished data from China Coal Processing & Utilization Association.

Fig. 1. Production of coal in China as a proportion of global coal production. Source: BP statistical review of world energy 2014.

1.4. China’s energy efficiency status quo During the first three years of the Twelfth Five Year Plan, Chinese coal companies installed advanced energy-saving technology and equipment, eliminated obsolete processes and products, and adopted new fuel and electricity saving methods during the coal production process, which saved 4.3 Mtce. This is only 1% of energy consumption saved. This unsatisfactory result may be due to the following reasons: lack of appropriate energy-efficiency techniques and poor auditing of mining processes like ventilation, hoisting and drainage. In addition there is also a lack of energysaving management policies and no technological development.

1.5. Paper structure This paper uses energy efficiency benchmarking to explore potential energy efficiency measures during coal mining, and pioneers the establishment of a comprehensive benchmarking system for coal mining energy efficiency. Three aspects of issues must be

N. Wang et al. / Applied Energy 169 (2016) 301–308

dealt with. The first issue involves the ambiguity of the benchmarking range: inter-industry or inter-enterprise? Product-based benchmarking or process-based benchmarking? The second issue relates to the absence of an energy efficiency benchmarking indicator system. The final issue refers to the lack of a unified benchmarking standard. Consequently, this paper uses energy benchmarking examples from other industries and preestablished energy efficiency standards in the coal industry. Based on an analysis of China’s energy situation and energy efficiency benchmarking, this paper uses product-based benchmarking and process-based benchmarking to create a benchmarking methodology which has the following properties: a unified energy efficiency benchmarking indicator system developed in accordance with related standards. A solution to the problem of being limited to a single per unit of product produced energy consumption benchmarking system. We also established an inter-enterprise energy efficiency benchmarking system for coal production, confirmed energy efficiency reference values and applied our energy efficiency benchmarking system to the Yankuang Group. It is a major energy company in China that ranked the 16th among China’s Top 100 Coal Companies. Finally the paper calculates the energy saving potential of China’s coal industry.

2. Methodology 2.1. Methodology selection Energy-efficiency benchmarking can be used as a tool to compare the performance of a company with that of its competitors and to estimate energy-saving potential [26,27]. Currently, industrial energy efficiency is primarily analyzed through the application of energy indicators and energy benchmarking [17,27–32] to calculate energy-efficiency potential. Energy efficiency indicators for comparison between countries (benchmarks) have been developed for industry, transport and construction [33,34] and are used in the 2009 IEA publications. The concept, definition and importance of energy-efficiency indicators are discussed in Haas [35]. Chung et al. [36] reviewed what kinds of mathematical methods are used in developing benchmarking systems, the properties of these methods, and how to classify two kinds of benchmarking systems: public benchmarking and internal benchmarking. The primary role of industrial energy benchmarking is to help improve energy efficiency and reduce carbon dioxide emissions. It is served as a set of valuable tools for energy management in government as well as private sections [37]. Energy benchmarking can be classified as product-based energy benchmarking and process-based energy benchmarking. Product-based energy benchmarking at the plant or sector level helps to determine the gap between the plants or sectors and to estimate the overall potential for energy efficiency improvement. Process-based benchmarking provides insights into where the major energy saving potential actually is and which areas or processes need to be improved [9]. This paper constructs energy efficiency benchmarking indicator systems, including indicators related to product-based energy benchmarking and process-based benchmarking. These correspond to product-based indicators and process-based indicators. Internal benchmarking includes both product-based and process-based indicators, which register changes in an enterprise’s energy consumption. Industrial benchmarking only includes product-based indicators, reflecting the annual fluctuation of industrial energy efficiency. The indicator standards of coal production are based on questionnaires and currently available standards. This paper also analyzes the benchmarking results for the energy-efficiency

303

potential of the coal industry, taking the eight coal mines owned by Yankuang Group as an internal benchmarking study case. 2.2. Indicator construction Coal production is a resource exploiting industry, so it is highly dependent on the distribution of coal and the unique conditions of different coal seams. Differences in mining capacity, development method, mining technology, equipment level, processing capability and transportation requirements result in varied levels of energy consumption in different coal mines. Therefore, process-based energy efficiency benchmarking could mitigate the influence of different conditions on energy consumed during coal production, and be able to tap latent energy reduction potential at the operational level. Fig. 2 shows that energy consumption during coal production is made up of complex factors. Product-based energy consumption indicators display levels of energy utilization in the whole coal mining industry. This helps us understand the general level and trends of energy consumption in the coal industry. No matter what, energy consumption rises with increased mine depth, so a single product-based energy efficiency indicator is not compatible with coal mining. Thus, the introduction of process-based energy efficiency indicators is necessary. Process-based energy efficiency measures ventilation, hoisting, drainage, pressure ventilation and transportation, which account for over 90% of energy consumption in coal production. Transportation refers to mining face and mining area transportation, as well as transportation of equipment like the belt conveyor, scraper conveyor and cable haulage. These are all different depending on the size of the mine face and area, so the calculation of energy consumption is difficult. Therefore, this paper takes the first four indicators to measure energy consumption (see Table 2). 2.3. Definitions of energy efficiency indicators Generally, the energy efficiency of equipment or an operation is defined as the ratio of useful work done (energy output) to the input energy [38]. The calculation of product-based or processbased energy efficiency indicators follow this approach. 2.3.1. Product-based energy efficiency indicators 2.3.1.1. Energy efficiency of raw coal production. Energy efficiency of raw coal production is the total energy consumed by using coal, electricity, oil and gas for coal production (tunneling, mining, ventilation, hoisting, drainage, air pressure, transportation and gas drainage). It excludes the energy consumed in coal washing, office districts and living quarters.

EEcp ¼ CEC=CP

ð1Þ

where EEcp is the energy efficiency of raw coal production kilogram coal equivalent (kgce/t). CEC is the comprehensive energy consumption of raw coal (kgce), and CP is total raw coal production (t). 2.3.1.2. Electricity efficiency during coal production. Electricity efficiency during coal production is the total amount of electricity used for raw coal production, excluding the electricity consumed in coal washing, office districts and living quarters.

EEel ¼ El C=CP

ð2Þ

where EEel is the electricity efficiency during coal production (kW h/ t). El C is the electricity consumed during coal production (kW h), and CP is total coal production (t).

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Integrated Design

Natural Factors

Working Layout

Geological Structure

Tunnel Layout

Coal Seam Development Method Water Treatment

Methane gas

Mine Water

Waste Treatment Ventilation Hoisting Drainage Air Pressure

Routinemaintenance

Coal recovery

Energy consumption of coal production

Transportation Energy Management

Allocation Eliminating obsolete equipment

Five System Staffing

Energy Conservation Technology Transformation Management

Equipment

Fig. 2. The general structure of energy consumption during the production process in the coal industry.

Table 2 An energy efficiency indicator system for internal benchmarking in coal production. Internal benchmarking

Indicators

Abbreviation

Unit

Product-based energy efficiency (Industrial Benchmarking)

Energy efficiency of raw coal production Electricity consumed in raw coal production

EEcp EEel

kgce/t kW h/t

Process-based energy efficiency

Main ventilation system Main hoisting system Main drainage system Air pressure system

EEv EEh EEd EEp

kW h/M m3 Pa kW h/t h m kW h/t h m kW h/M m3 Pa

2.3.2. Process-based energy efficiency indicators Process-based energy efficiency refers to the ratio of total energy consumption and total workload in the coal production. Namely, the energy consumed per unit of work. The formula of process-based energy efficiency is:

PEEpb ¼ TC=TW

ð3Þ

where PEEpb is a process-based energy efficiency indicator for the statistics period, TC is the total energy consumption of a process, and TW is the total workload of the process.

tilator (kW h). Qi is the ventilation quantity of the ith ventilator (m3), Pi is the pressure of the ith ventilator (Pa), and n is the number of ventilators in operation. 2.3.2.2. Main hoisting system in vertical shaft. The energy efficiency of the main hoisting system refers to the amount of electricity consumed for every ton of coal to raise a load by 100 m.

EEh ¼

102  E K Q H

ð5Þ

ð4Þ

where EEh is the energy efficiency of main hoisting system for the statistics period (kW h/t hm), and E is the electricity used in the main hoisting system house (kW h). Q is the quantity of raw coal raised during hoisting (t), H is the height of the hoisting shaft (m), and K is the conversion coefficient of the effective height of the main hoisting system [39].

where EEv is the energy efficiency of the main ventilation system (kW h/M m3 Pa), and Ei is the electricity consumption of the ith ven-

2.3.2.3. Main drainage system. The energy efficiency of the main drainage system refers to the amount of electricity used to hoist

2.3.2.1. Main ventilation system. The energy efficiency of the main ventilation system refers to the amount of electricity consumed per 1 trillion m3 of wind discharged from the main ventilation system.

106  EEv ¼ Pn

Pn

i¼1 Ei Q i¼1 i P i

305

N. Wang et al. / Applied Energy 169 (2016) 301–308 Table 3 The standard of energy consumption in coal production. Standards type

Items

Publisher

Implementation date

Product-based standards

Quotas for comprehensive energy consumption of raw coal production (DB37/8322007) Quotas for electrical consumption of raw coal production (DB37/831-2007)

Shandong Bureau of Quality and Technical Supervision Shandong Bureau of Quality and Technical Supervision Liaoning Bureau of Quality and Technical Supervision

2008.1.1

State Administration of Work Safety

2009.1.1

State Administration of Work Safety

2009.1.1

NDRC

2006.12.1

NDRC

2006.12.1

Quotas & a calculation method for comprehensive energy consumption during the production of raw coal (DB21/T1841-2010) Process-based standards

Monitoring methods and regulations for energy conservation of coal mine main ventilation systems (MT/T 1071-2008) Monitoring methods and regulations for energy conservation of coal mine main elevating belt conveyor (MT/T 1070-2008) Monitoring methods and decision regulation for energy conservation of coal mine winding engines(MT/T 1001-2006) Monitoring methods and decision regulation for energy conservation of coal mine main drainage systems (MT/T 1002-2006)

2008.1.1 2010.12.16

one ton of mine drainage 100 m, under normal conditions of operation.

102  EEd ¼ Pn

Pn

i¼1 Ei Q H i¼1 i i ci

ð6Þ

where EEd is the energy efficiency of the drainage system (kW h/ t hm), and Ei is the electricity consumption of the ith pump (kW h). Qi is the water quality of the ith pump (t), Hi is the vertical height of the ith pump (m), ci is the energy consumption correction factor of the ith pump [39] and n is the number of pumps used. 2.3.2.4. Main pressure air system. The energy efficiency of the main air pressure system refers to the electricity consumed, when compressing one cubic meter of air and increasing pressure by 1 MPa.

EEp ¼

2:398  E lnð10P g Þ  Q

ð7Þ

Here EEp is the energy efficiency of the air pressure system (kW h/m3 MPa), E is the electricity consumption of the air pressure system (kW h), Q is the quantity of nominal air displacement in the air pressure system (m3), and Pg is the average absolute pressure of the air pressure system entrance in the operating condition (MPa). 2.4. Benchmarking standards and reference values 2.4.1. Benchmarking standards Research on the coal mine process-based standards was first conducted in 1992. The Coal Industry Energy Conservation Center undertook a research project called ‘‘Research on the Coal Enterprises Process Energy Consumption”, from which the Major Process Energy Consumption for Coal Mines was compiled. This contains information about the main energy consuming processes of coal production. In addition, state and local governments established partial standards on coal production and energy consumption (Table 3). Table 3 shows that product-based standards mainly appear in Shandong province and Liaoning province. Without the grade indicators classification, it is difficult to determine the energy consumption level in the coal mining enterprises’ benchmarking processes. In addition, process-based standards only examine monitoring methods and decision regulations, and neglect to evaluate the energy-efficiency of the major energy consumption indicators. This is because coal mining is a resource extractive industry without systematic benchmarking management and advanced standards, caused by complex coal seam locations, complicated production processes and the strict security demands in the mining industry.

Fig. 3. 50 Large-scale coal enterprises class.

2.4.2. Reference values In this paper, energy efficiency indicators are divided into three levels (Fig. 3). Level one is the national advanced level, encompassing enterprises within the top 10% of energy consumption distribution and characteristics of coal mining. Level two is the industry advanced level that refers to companies within the 10–25% range. The third level is the industry average level that includes enterprises within the 25–50% range. The energy-efficiency of coal mining indicator reference values is determined from the statistical data of 50 large-scale coal enterprises. Other reference values and their sources are referred to in Table 4. The total coal production from these 50 large-scale coal enterprises in 2012 was 18.33 hundred million tons, which constituted 46.5% of total yearly domestic coal production (39.45 hundred million tons).

3. Case study and results 3.1. Case study of Yankuang Group The Yankuang Group is one of the largest energy companies in China, and its main operation sites are eight coal mines in eastern China. Table 5 shows their energy efficiency in 2010. Table 5 analyzes the energy consumption status of the eight coal mines. The results show three benchmarking indicators, including enterprise average energy efficiency, energy efficiency benchmarks and backward energy efficiency. The comparative analysis between enterprise backward energy efficiency and benchmarking energy efficiency shows that there is a big gap

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Table 4 Reference values of energy efficiency benchmarking indicators. Indicators

Dongtan

Classification First level

Product-based energy efficiency EEcp 55 515 EEel [14] EEv

Jisan

Axial Centrifugal

EEh EEd EEp

50.360 50.360 50.401 50.453 50.107

Second level

Third level

5–7 15–20

7–12 20–30

0.361–0.400 0.361–0.380 0.401–0.441 0.454–0.496 0.108–0.114

0.401–0.520 0.381–0.500 0.442–0.500 0.497–0.560 0.115–0.130

Yangcun Beisu Jier Baodian Gas Oil Electricity Coal

Xinglong Nantun

between the enterprise energy efficiency values. Statistics show that the energy efficiency of Beisu coal mine is the lowest of all eight coal mines, it has the highest energy-efficiency potential (47%) compared to the benchmark. This may because Beisu coal mine is a resource-depleted coal mine, compared to the other 7 coal mines. Compared to Xinglong coal mine, Baodian coal mine could improve its energy efficiency by 38.5%. In terms of process-based energy efficiency, Baodian coal mine could improve its ventilation and air pressure system energyefficiency by 45% and 31% compared with Jisan coal mine and Dongtan coal mine. Compared to Jisan coal mine and Xinglong coal mine, Beisu coal mine could improve its main hoisting system’s energy efficiency by 34% and its main drainage system’s energy efficiency by 14%. Fig. 4 shows energy consumption by type for eight mines of Yankuang Group. Electricity is the primary energy used for tunneling, mining, ventilation, hoisting, drainage, air pressure and transportation. Coal and gas are used in pithead heating- only Beisu and Yangcun use coal, while all others use natural gas. Oil is used for raw coal and coal gangue transportation, taking up only a very small portion. Fig. 5 shows the total energy consumption in all eight mines by process type. Electricity accounts for 80% of total energy consumption. Gas accounts for about 17%, mainly used for pithead heating. Oil and coal, conversely, account for a very small portion of total energy consumption, equaling 2.5% and 1.1% respectively. Fig. 6 shows that the average amount of energy-efficiency potential available for the Yankuang Group is 22.77%. For electricity consumed this figure stands at 26.75%. For process-based energy efficiency, the energy-saving potential of the main ventilation system and the air pressure system is more than 20%, while that of the main hoisting system and the main drainage system is 7.56% and 16.05%. Baodian coal mine and Beisu coal mine have low process-based energy efficiency, so improving these mines will help raise overall energy efficiency.

0%

20%

40%

60%

80%

100%

Fig. 4. Energy consumption by type for eight coal mines.

Fig. 5. Total energy consumption by type.

3.2. China’s potential and policies In the past nine years, China’s total energy consumption of coal production increased from 43 Mtce in 2005 to 61.5 Mtce in 2013. This is based on the estimation of energy consumption in large coal enterprises whose total yield is 1.833 billion tons of coal, which is 54% of China’s coal production, and is shown in Fig. 7 Energy efficiency of raw coal production shows a downward trend to 16.7 kgce/ton of raw coal in 2013, which is a 14% fall compared to 2005.

Table 5 An energy efficiency assessment of the Yankuang Group’s coal mines. Indicators

EEcp

EEel

EEv

EEh

EEd

EEp

Nantun Xinglong Baodian Jier Beisu Yangcun Dongtan Jisan Average (A)

4.3 3.46 3.81 3.74 6.54 5.03 3.65 5.29 4.48 First 3.46 First 6.54 3.08 47.09%

22.6 14.69 14.21 22.31 23.11 21.46 16.18 20.6 19.4 Second 14.21 First 23.11 8.9 38.51%

0.362 0.406 0.64 0.397 – 0.473 0.473 0.351 0.44 Third 0.351 First 0.64 0.289 45.16%

0.418 0.379 0.42 0.41 0.441 0.397 0.397 0.414 0.41 Second 0.379 First 0.441 0.062 14.06%

0.348 0.394 0.42 0.4 0.486 0.351 0.351 0.319 0.38 First 0.319 First 0.486 0.167 34.36%

0.098 0.106 0.11 0.108 0.089 0.076 0.076 0.104 0.1 First 0.076 First 0.11 0.034 30.91%

Benchmark (B) Backward (P1) Maxim potential

Value Grade Value Grade Difference (P1–B) Potential (%)

N. Wang et al. / Applied Energy 169 (2016) 301–308

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4. Discussion and conclusion 22.77%

26.75%

20.23%

7.56%

16.05%

24.00%

Fig. 6. Energy efficiency assessment and average potential analysis.

Fig. 7. Total energy consumption and energy efficiency of China’s coal production.

Assuming that the energy efficiency of raw coal production in the whole industry could reach the Third level (7–12 kgce/t), national energy savings from coal production would be 15.98– 32.98 Mtce. This is the equivalent of reducing 42–87 Mt of CO2 emissions. This will contribute to achieving the goal of ‘‘40–45%” of CO2 reductions in 2020. The following measures should be taken to help achieve these goals. (1) There are some gaps in the research on energy efficiency of coal production across the whole life cycle of the coal industry. The government should strengthen energy management research across the whole lifecycle, and design macro-level energy efficiency policies. To implement an energy information monitoring system, timely feedback should be given to the industry’s management department, in order to find the problems through benchmarking and devise solutions. (2) Energy efficiency management needs to be strengthened. Enterprises should establish objective indicators for local coal mines and develop specific energy saving measures and detailed energy efficiency evaluation rules. Coal mines must also optimize the indicator management process, increase the distribution of measuring instruments and enhance oversight and management of energy consumption equipment. (3) Coal mines must optimize the production system. Enterprises should scientifically optimize the power supply and distribution system, shorten the power supply radius, reduce energy loss in transmission lines, improve equipment efficiency, decrease the empty-load ratio and prevent power mismatches. (4) Coal mines need to update products and technology. Enterprises should remove obsolete machines with high energy consumption, and install energy efficient AC synchronous permanent magnet motors, and promote the use of technologies such as high-voltage dynamic reactive power compensation and variable frequency regulation.

A single product-based energy efficiency assessment method has some disadvantages. Product-based energy efficiency rises in accordance with an increase in mining depth and complexity, which is the case at Beisu coal mine. In order to address the shortcomings of production based energy efficiency indicators and standards, this paper developed an energy efficiency benchmarking methodology, as well as benchmarking indicators. This makes up for the absence of a system of energy efficiency indicators and a standard benchmarking system. The method we use provides analysis of process-based energy efficiency status. This information is very useful to enterprises, who pay attention to energy audits, as it helps them discover energy consumption, improve energy consumption management and implement technology upgrades. Comparing results with the Shandong province quota, Yankuang Group has a significantly smaller EEcp . The reason is that Yankuang Group is a major coal producer in China that has advanced energy saving technologies and energy management in comparison with the Shandong average. Using Yankuang Group as a case study, this paper provides enterprise benchmarking, as well as maximum and average potential energy efficiency analysis. The results show that the electricity consumption during raw coal production can be reduced by 26.75%. Coal mines should implement stringent energy efficiency measures. These measures must extend to the whole industry. If energy efficiency reaches the Third level, we estimate that energy savings in national coal production will be 15.98–32.98 Mtce, accounting for about 26–55% (average 40.8%) of coal mining energy consumption. This is close to the US mining industry’s energy efficiency potential (46%) as estimated by the DOE. This will make an important contribution to China’s energy efficiency promotion. To achieve this goal, we recommend three kinds of measures: strengthening energy efficiency management, optimizing the production system, and updating products and technology implementation. Acknowledgments The authors gratefully acknowledge the financial support from the National Natural Science Fund for Outstanding Scholars of China (No. 71522011) and the ‘‘Twelfth Five-Year” National Key R&D Program (No. 2012BAC20B10) of China. The contents of this paper reflect the views of the authors and do not necessarily indicate acceptance by the sponsors. Thank you Mr. Djavan De Clercq and Mr. Jason Lee for providing language help and proof-reading the article. References [1] Zhang KF, Liu ZL, Wang YY, Li YX, Li QF, Zhang J, et al. Flash evaporation and thermal vapor compression aided energy saving CO2 capture systems in coalfired power plant. Energy 2014;66:556–8. [2] Bhatt MS. Energy efficiency and greenhouse emission burden from coal-fired electric power plants – a case study of the Indian power sector. Energy Sources 2000;22:611–23. [3] Man Y, Yang SY, Zhang J, Qian Y. Conceptual design of coke-oven gas assisted coal to olefins process for high energy efficiency and low CO2 emission. Appl Energy 2014;133:197–205. [4] Zhang LJ, Xia XH, Zhang JF. Improving energy efficiency of cyclone circuits in coal beneficiation plants by pump-storage systems. Appl Energy 2014;119:306–13. [5] Santosh KR, Aditya KP, Sneha R, Ghosh AK. Clean coal technology to improve environmental quality and energy efficiency. J Mines Met Fuels 2009;57:267–74. [6] Zhao XL, Yang R, Ma Q. China’s total factor energy efficiency of provincial industrial sectors. Energy 2014;65:52–61. [7] Maryam AO, Kwame AO. Statistical methods for evaluating the effect of operators on energy efficiency of mining machines. Min Technol 2014;123:175–82.

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